Note CLXXVIII — Chapter V
P. W. (Patrick Weston) Joyce translation
] The "Three Tonns or Waves of Erin" were the Wave of Tuath outside the mouth of the river Bann, off the coast of Derry; the Wave of Rury in Dundrum Bay, off the county Down; and the Wave of Cleena in Glandore Harbour in the south of Cork. In stormy weather, when the wind blows from certain directions, the sea at those places, as it tumbles over the sandbanks, or among the caves and fissures of the rocks, utters a loud and solemn roar, which in old times was believed to forebode the death of some king.
The legends also tell that the shield belonging to a king moaned when the person who wore it in battle—whether the king himself or a member of his family—was in danger of death: the moan was heard all over Ireland; and the "Three Waves of Erin" roared in response. See "Irish Names of Places," Vol. II., Chap. XVI.